Multiple studies have established that bright light therapy is effective in alleviating symptoms of winter depression (seasonal affective disorder, or SAD). Light units used for treating SAD in the past have generally emitted polychromatic white light of highly variable spectral properties. Although several studies have attempted to test the effectiveness of specific wavelengths of red, blue and green light for treatment of SAD, the devices used in those studies employed relatively broad bandwidths of light. With the technological advancements in light emitting diodes (LEDs), the production of new light treatment equipment with much narrower bandwidths of light is possible. A recently completed action spectrum demonstrated that 446-477 nm is the most potent wavelength range for regulating melatonin secretion. These results suggest that a novel opsin photopigment, separate from the four classical visual opsins, mediates the effects of light on melatonin and raises the possibility that light treatment for SAD may share a common photoreceptor system and therefore, a similar spectral sensitivity. The specific aims of this proposed study are to: 1) produce an LED panel light box which emits narrow band light stimuli with a 470 nm peak (30 nm half-peak bandwidth) for light treatment of SAD; 2) confirm safety of this device through a hazard analysis based on accepted federal and industrial guidelines, and 3) use this device to test the hypothesis that light stimuli concentrated in the 470 nm range is therapeutically effective in treating SAD. Therapeutic efficacy will be tested in a double-blind, randomized cross-over study design comparing a narrow band LED light source with a spectral peak at 470 nm (30 nm half-peak bandwidth) to a narrow band dim red light placebo control with peak emission at 700 nm. Demonstration of efficacy of relatively narrow bandwidth blue light will pave the way for future studies in which this spectral range may be further tested for SAD treatment and circadian rhythm dysfunctions in order to maximize therapeutic benefits with lower light intensities and therefore, fewer side effects.